Anterior Cruciate Ligament – Anatomy

“In My Office”

‘I’ve been told that I’ve torn the ACL in my knee – what is it and why is it so significant?’

The ACL or anterior cruciate ligament is one of the primary stabilizers in your knee. Ligaments have a fixed length and connect two bones of a joint. Each of the joints in the body has multiple ligaments, which stabilize and help to control and provide for smooth, gliding motion. The knee is inherently unstable due to the lower leg (tibia) being a flat, table-top like surface on which the ‘knuckles’ or runners of the thigh bone (femur) rest and roll while bending the knee. Further, the tibia and femur are able to rotate independently of each other. The ACL courses between the two thigh runners of the femur and may be torn if twisting of the knee is excessive or the notch in the femur from which it exits is particularly narrow. Of the ligaments in the knee, the ACL is one of the most commonly injured during athletic activities. Planting your foot and making a rapid change of direction can result in the ligament being ‘guillotined’ in the narrow notch. Impact to the knee resulting from contact with another player while your foot is planted can also lead to a torn ACL. Occasionally, an abrupt stop, while running can have a similar result. When the ACL is torn or deficient, excessive motion of the femur on the tibia occurs and the knee feels unstable. The instability can lead to the unexpected buckling or giving way of your knee, sometimes with little warning. Sports that involve running along with cutting and pivoting, such as football, soccer, and basketball, lead to a higher rate of ACL injury. It is relatively common for additional structures in your knee to be injured at the time that the ACL tears. Other knee ligament damage as well as meniscus tears are commonly associated with an anterior cruciate ligament tear. The meniscus (there are two in each knee) are tough, gristly ‘C’ or ‘O’ shaped structures that lie between the tibia and femur, and provide a protective cushion and weight-distributing function in the knee. Meniscus damage and loss can result in a more rapid wear of the articular, or ‘tread cartilage’ in your knee leading to eventual degenerative or osteoarthritis. As is apparent, the ACL is essential for the normal healthy function of your knee and its loss can have serious consequences. It is important to have your knee evaluated if you sustain an injury.